Embargoed to 0001 Wednesday December 11''File photo dated 29/10/13 of David Cameron who is calling for Britain to take a worldwide lead in dementia research with a doubling of investment by government and the private sector. PRESS ASSOCIATION Photo. Issue date: Wednesday December 11, 2013. The Prime Minister is hosting the G8 dementia summit in London which is expected to agree to a package of measures on international information-sharing and collaboration in research. In a keynote address, he will stress the importance of achieving scientific breakthroughs in order to slow down, or even prevent, the onset of the debilitating brain condition now believed to afflict 36 million people around the world. See PA story HEALTH Dementia. Photo credit should read: Dominic Lipinski/PA Wire